If you make the payment through EFTPS you don't need to mail a 1040-ES. EFTPS doesn't have the best user interface I've seen, but you should be able to figure it out once you have your PIN. Just remember that you're making an estimated tax payment for 2012.

Phil's last statement can't be emphasized enough. If you mistkenly enter the payment as a 2013 estimated payment, there is no way to move it back to 2012. It's against IRS rules.